Add support for numpy float16

Related to: aidge_onnx!131 (comment 3986247)

pybind doesn't support half type https://github.com/pybind/pybind11/blob/master/include/pybind11/numpy.h#L202.

So this require to add some boilerplate as described here: https://github.com/pybind/pybind11/issues/1776#issuecomment-491514980